JPH04355906A - Choke coil and noise-reducing device for switching power supply - Google Patents

Abstract

PURPOSE:To obtain the noise-reducing device for choke coil and a switching power supply which can be made small in size at low cost by increasing the leakage inductance of a common mode choke coil. CONSTITUTION:A core 21 with which a closed magnetic circuit is constituted, two coils 11 and 12 wound on the different part of the above-mentioned core 21, and a bypass means 22, with which a part of the magnetic flux generated by the current conducted to the coils is bypassed independent of the closed magnetic circuit, are provided in the title noise-reducing device.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise reduction device used in switching power supplies and the like, and more particularly to an improvement in the structure of the noise reduction device which is small in size and highly effective in reducing conduction noise.

0002

2. Description of the Related Art In a switching power supply device, a noise reduction device (noise filter circuit) is used, for example, as disclosed in Japanese Patent Laid-Open No. 2-79766 proposed by the present applicant. FIG. 16 is a circuit diagram of a conventionally known switching power supply device. In the figure, in a filter circuit 10, a commercial AC power source is connected to a level terminal L and a neutral terminal N, and a ground terminal G is grounded. Diode bridge DB rectifies the alternating current output from filter circuit 10, and smoothes it with capacitor C1. A direct current smoothed by a capacitor C1 is applied to the primary winding n1 of the transformer T, and is turned on and off by a switching element Q such as an FET. Then, a switching signal is induced in the secondary winding n2 of the transformer T, so it is rectified by the diodes D1 and D2, the high frequency component is removed by the choke coil L2, and the electricity is stored in the capacitor C2 and sent to the load side. A DC current of a predetermined voltage Vout is supplied. The output voltage stabilizing circuit detects the output voltage Vout and sends an on/off control signal to the switching element Q so that the output voltage Vout becomes a predetermined constant voltage. Although the filter circuit 10 is provided before the rectifying and smoothing circuit including the diode bridge DB and the capacitor C1, it may be provided after the rectifying and smoothing circuit, or may be provided both before and after the rectifying and smoothing circuit.

FIG. 17 is a detailed circuit diagram of the filter circuit 10 mentioned above. The across-the-line capacitor CX1 connects the level terminal L and the neutral terminal N, and a discharge resistor R1 is connected in parallel with it. Common mode choke coil L1 is across-the-line capacitor CX1
Connected to the rear stage, it reduces common mode noise and normal mode noise. The across-the-line capacitor CX2 is connected after the common mode choke coil L1, and the capacitor CY is connected in parallel with this.
1, CY2 is connected. Capacitor CY1, CY
2 has the connection point of both grounded to reduce common mode noise. The main function of the filter circuit 10 is to suppress noise conducted and leaked from the switching power supply to the AC power supply side.

FIG. 18 is an explanatory diagram of noise in the vicinity of the filter circuit 10. The filter circuit 10 has P1 as an input terminal.
, P2, and has output terminals P3 and P4. An AC power supply 2 is connected to the input terminals P1 and P2, and a switching power supply 4 is connected to the output terminals P3 and P4. The switching power supply 4 is grounded via an impedance Z1.

Here, if the switching power supply 4 is a noise source, there are two types: common mode noise current i1 and normal mode noise currents i2 and i3. As shown by the broken line in the figure, the common mode noise current i1 is caused by impedance Z.
1 and the ground and returns to the switching power supply 4. As the impedance Z1, there is a capacitor between the can case of the switching element Q and the heat sink, etc. The normal mode noise current i2 flows from the AC power supply 2 to the filter circuit 10, as shown by the solid line, and the normal mode noise current i3 flows from the switching power supply 4 to the filter circuit 10, as shown by the dashed line. Both of them flow in a route that goes back and forth between two signal lines connecting the AC power supply 2 and the switching power supply 4.

Next, the noise reduction of the filter circuit 10 is divided for each noise. Common mode noise current i1 is generated by common mode choke coil L1 and capacitors CY1 and C.
It is reduced by the action of Y2. That is, the inductance of the common mode choke coil L1 acts as a large impedance to the common mode noise current i1. Further, since the common connection point of the capacitors CY1 and CY2 is grounded, the common mode noise current i1 is circulated to the switching power supply 4 side, and is prevented from leaking to the AC power supply 2 side. The normal mode noise current i2 is generated by the AC power supply 2 due to the action of the across-the-line capacitor CX2.
The normal mode noise current i3 is returned to the source on the switching power supply 4 side by the action of the across-the-line capacitor CX1, and the normal mode noise current i3 is returned to the source on the switching power supply 4 side, and the normal mode noise current i3 is returned to the source on the switching power supply 4 side by the action of the across-the-line capacitor CX1.
The total amount of malmode noise currents i2 and i3 is reduced.

FIG. 19 shows a common mode choke coil L1.
FIG. Common mode choke coil L1
consists of coils 11 and 12 and a core 13 wound in common with these coils, and the core 13 forms a closed magnetic circuit. The main inductance is generated by the magnetic flux φ1 interlinking with both coils 11 and 12, and the leakage inductance is caused by the magnetic flux φA, φB, φC interlinking with only one coil.
This is caused by The main inductance contributes to the attenuation of the common mode noise current i1, and the leakage inductance contributes to the attenuation of the normal mode noise currents i2 and i3.

[0008]

[Problems to be Solved by the Invention] However, since the purpose of the conventional common mode choke coil L1 is to increase the main inductance, the leakage inductance is a secondary value determined by the number of turns required to obtain the main inductance. It was nothing more than Therefore, the value of the leakage inductance is not sufficient to attenuate the normal mode noise current, and the across-the-line capacitors CX1 and C
This was dealt with by increasing the capacity of X2. As a result, the size of the filter circuit 10 increases, resulting in an increase in cost, which becomes a major problem when noise regulation is required, such as in a switching power supply, and a small, low-cost product is desired.

The present invention has solved these problems, and provides a choke coil and a switching power supply device that can reduce the size and cost of the filter circuit by increasing the leakage inductance of the common mode choke coil L1. The present invention aims to provide a noise reduction device.

0010

[Means for Solving the Problems] The invention of claim 1 which achieves such an object comprises a core (21) constituting a closed magnetic circuit, and two coils (1) wound around different parts of this core.
1, 12), and a bypass means (22) that is provided with a magnetic material inside the closed magnetic path of the core and bypasses a part of the magnetic flux generated by the current flowing through the coil independently of the closed magnetic path. It is something to do.

[0011] The invention according to claim 2 includes a core (45) constituting a closed magnetic circuit with a constant cross-sectional area (a), two coils (11, 12) wound around different parts of this core, A part of the magnetic flux generated by the current flowing through the coil is bypassed independently of the closed magnetic circuit, which is provided with a magnetic material inside the closed magnetic circuit of the core and separates the two coils from each other. Bypass means (46, 47) are provided. The cross-sectional area of the bypass means is set to be twice the cross-sectional area of the core or slightly smaller than this.

[0012] The invention according to claim 3 includes a core (45) constituting a closed magnetic circuit with a constant cross-sectional area (a), two coils (11, 12) wound around different parts of this core, A part of the magnetic flux generated by the current flowing through the coil is bypassed independently of the closed magnetic circuit, which is provided with a magnetic material inside the closed magnetic circuit of the core and separates the two coils from each other. Bypass means (48) is provided. The magnetic material of the bypass means is made higher than the saturation magnetic flux density of the magnetic material of the core, and the cross-sectional area of the bypass means is made smaller than the cross-sectional area of the core.

[0013] In a second aspect of the present invention, the choke coil according to claim 1, 2 or 3 is connected to an AC power source, and the applied AC current is converted to DC by a rectifying and smoothing circuit, and the DC current is This is characterized by converting the voltage into a DC voltage of a predetermined voltage using a switching power supply and supplying it to the load side. Note that the connection relationship between the choke coil and the rectifying and smoothing circuit may be reversed.

[0014]

[Function] Each component of the present invention has the following function. The bypass means acts so that a part of the magnetic flux generated by the current flowing through the coil bypasses magnetic paths other than the closed magnetic path. This therefore increases the leakage flux, ie the leakage inductance of the common mode choke coil. Therefore, if such a choke coil is used as a noise reduction device for a power supply device, it will reduce the normal mode noise current.
Since an inductance component is generated, this noise current can be reduced.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below with reference to the drawings. Figure 1
FIG. 1 is a diagram showing a first embodiment of a common mode choke coil according to the present invention. In the figure, a ring-shaped core 21 constitutes an annular closed magnetic path and is made of a magnetically permeable material. The protrusions 22 and 23 are magnetically permeable members provided in a direction protruding toward the center of the ring-shaped core 21, and constitute a bypass path for the annular closed magnetic circuit, which the inventors call a metatarsal core. . This protrusion is part of the core. coil 11
, 12 are wound around two areas of the ring-shaped core 21 separated by the protrusions 22 and 23, respectively. Protrusions 22, 23
An air gap is provided between them. This is because if an air gap is not provided, leakage magnetic flux (magnetic flux passing through the protrusions 22 and 23) will become too large, and the original operating current supplied from the AC power supply 2 (see FIG. 18) to the switching power supply 4 will This is because it becomes saturated. but,
If the magnetic material of the protrusions 22 and 23 is made of a material with low magnetic permeability, there is no need to provide this air gap.

The induction increasing effect of the device thus constructed will now be explained. FIG. 2 is an inductance model of the common mode choke coil shown in FIG. 1. In the coils 11 and 12, the magnetic fluxes φB leaking to the outer edge side of the ring-shaped core 21 are assumed to be the same for convenience. The magnetic flux leaking inside the ring-shaped core 21 is defined as φA'. At this time, when comparing the size relationship with the inner leakage magnetic flux φA of the conventional type not having the protrusions 22 and 23, the leakage magnetic flux is larger in the type having the protrusions 22 and 23. φA<φA'
(1) Next, when comparing the outer edge leakage magnetic flux φB and the inner leakage magnetic flux φA', the following equation holds because the air path taken by the magnetic flux φB is extremely large (that is, the magnetic resistance is extremely large). ing. φB<<φA'
(2)

FIG. 3 is a diagram showing a model of the space through which the magnetic flux that generates leakage inductance passes. Divide the space through which magnetic flux passes into the following three areas. Region E: A partial region of the region surrounded by the core 21 excluding the portions where the magnetic flux bypasses (22, 23 in FIG. 2 and their vicinity) F: Region E of the region surrounded by the core 21 Partial area G excluding: area outside the core 21

FIG. 4 is a magnetic equivalent circuit diagram of the device shown in FIG. 3, showing the magnetic circuit for the magnetic flux generated from one coil 11 (or 12) that generates leakage inductance. The magnetic resistance of regions E, F, and G when the projections 22 and 23 are not provided is that of air. Therefore, each magnetic resistance of each region E, F, G is RE,
Let RF and RG be. Ro is core 2, which is a closed magnetic path.
1, it is the magnetic resistance of the part where the leakage magnetic flux passes, and RE
, RF, and RG, and can be ignored. Further, Vm is the magnetomotive force caused by the coil, and is equal to the number of turns N of the coil multiplied by the current I flowing.

[0019] Here, if a bypass means is provided, the RF
becomes RF/μr. μr is the bypass means (
It is the effective relative magnetic permeability of the magnetic material and the air gap), and is 1<μr. When the leakage inductance before the bypass means is provided is L, and the leakage inductance after the bypass means is provided is L', the following relationship holds true. L={1/RE +1/RF +1/RG}・N
2 = {1/RF + (1/RE +1/RG
)}・N2 (3)
L'={1/RE +μr /RF +1/RG }
・N2 = {μr /RF + (1/RE
+1/RG)}・N2 (4
) N: Number of turns for each of coils 11 and 12

0
From equations (3) and (4), it can be seen that L<L'. That is, by providing the bypass means, the magnetic flux passing through the region F increased, and the leakage inductance increased. For example, if RE, RF, and RG are comparable and a core material with μr = 10 is used in region F, the leakage inductance will be four times as large. Further, if necessary, a desired leakage inductance can be obtained by providing an air gap in the bypass means or using a material with an appropriate relative permeability value. In this case, the impedance against normal mode noise current will increase, but the switching power supply (load) 4
There is no possibility that it will act as an impedance for the original power signal supplied to the circuit. While the original power signal has a commercial frequency of 50Hz or 60Hz, the frequency of the normal mode noise current that usually causes problems is 10kHz.
This is because the frequency bands are completely different.

Next, FIG. 5 shows a modification of the first embodiment of the present invention, in which a separator 26 made of a magnetic material is provided as a bypass means on a ring-shaped core 25 as a closed magnetic path. This separator 26 has two coils 1
It also has the effect of physically separating 1 and 12. In this figure, a separator 26 made of magnetic material is the bypass means.

FIG. 6 shows a second embodiment of the present invention, in which a square core is used. FIG. 6(a) shows an example in which a closed magnetic circuit is constructed by combining an E-shaped core 27 and an I-shaped core 28.
The central leg 29 of the shaped core forms the bypass means. FIG. 6(b) is an example in which two E-shaped cores 31 and 32 are combined. In FIG. 6(c), two U-shaped cores 33 and 34 are combined to form a closed magnetic path. The metatarsal core 35 is placed in this closed magnetic path to serve as bypass means.

Next, a specific measurement example for the second embodiment will be explained. Table 1 shows the UU type core {conventional example...Figure 6(c)
} with the metatarsal core removed from the configuration of
When using the EE type core {this example...FIG. 6(b)},
Actual measurement comparison data of leakage inductance is shown.

[Table 1] The common mode choke coil of the above example has a closed magnetic path length of 70 mm, a cross-sectional area of the closed magnetic path of 24 mm2, an air gap of 5 mm, and each coil 11 and 12 is wound with 90 turns. be. The main inductance is the same, but the leakage inductance is almost doubled.

FIG. 7 is an explanatory diagram of a third embodiment of the present invention. Using two U-shaped cores and one I-shaped core, coils 11 and 1
This figure shows a composite type in which coils 13 and 14 constitute a common mode choke coil with large leakage inductance, and coils 13 and 14 constitute a conventional common mode choke coil. In the example of this figure, the metatarsal core 38 as a bypass means is connected to the core 37 without providing an air gap. In this case, the material of the metatarsal core 38 is a magnetic material with low magnetic permeability.

FIG. 8 is an explanatory diagram of a fourth embodiment of the present invention. This is an example in which planar coils 15 and 16 are used as the coils. A middle core 40 as a bypass means is provided in the rectangular core 41 as a closed magnetic path.

FIG. 9 is an explanatory diagram of the fifth embodiment of the present invention.
The configuration of a phase common mode choke coil is shown. Three coils 17, 1 are arranged in a ring-shaped core 42 as a closed magnetic path.
8 and 19, and a Y-shaped metatarsal core 41 is provided as a bypass means. FIG. 10 is an explanatory diagram of a modification of the fifth embodiment of the present invention, in which an air gap is provided in the metatarsal core 43.

Next, the relationship between the dimensions of the core constituting the closed magnetic circuit and the bypass means provided in the present invention will be explained. FIG. 11 shows a sixth embodiment using two E-shaped cores shown in FIG. 6(b). In the figure, if the cross-sectional area of the portion constituting the closed magnetic path is a, the cross-sectional area of the bypass means 46, 47 is twice that, 2a.

Generally, the largest current in the normal mode is the original power current supplied from the AC power supply 2 to the switching power supply 4. If the leakage magnetic flux generated by all normal mode currents is φM, then the cross-sectional area a of the core 45 constituting the closed magnetic path can be designed in advance to a value that does not saturate with this φM. That is, since the number of turns N of the coils 11 and 12 and the value of the original power current supplied from the AC power supply 2 to the switching power supply 4 are known in advance,
The magnetic flux φM can be easily calculated. Then, as shown in the figure, twice the magnetic flux φM generated by the two coils 11 and 12 flows through the bypass means 46 and 47, so that the cross-sectional area of the bypass means 46 and 47 is set to the closed magnetic circuit cross-sectional area so as not to be saturated with them. It is set to 2a, which is twice the number.

FIG. 12 is an explanatory diagram of a seventh embodiment of the present invention. The core 45 is made by butting together two U-shaped members forming a closed magnetic path, and is made of, for example, Mn with a relative magnetic permeability of about 7500.
Use Zn-based ferrite or Fe-based amorphous. The metatarsal core 48 connects the middle of the core 45, and is preferably made of a magnetic material with a relative magnetic permeability of several tens to several hundreds and a saturation magnetic flux density of about 1 Tesla or more. For example, a 3% silicon steel plate has a relative permeability of 6 at a frequency of 100kHz.
00, a saturation magnetic flux density of 2.0 Tesla was obtained, and Fe
- A magnetic material such as Si-Al alloy sendust or pure iron may be used. Compared to the bypass means 46 and 47 of the sixth embodiment, a magnetic material with a high saturation magnetic flux density is used.

[0030] The operation of the apparatus configured as described above will be explained next. FIG. 13 is a diagram showing a model of the space through which the magnetic flux that generates leakage inductance passes. Divide the space through which magnetic flux passes into the following three areas. Region E*: A partial region surrounded by the core 45 excluding the part where the magnetic flux bypasses (the part near the gap when there is a gap with the metatarsal core 48) F*: Surrounded by the core 45 Partial region G* where magnetic flux is bypassed among the regions: region outside the core 45 Furthermore, the magnetic equivalent circuit diagram is shown in FIG. 4 for each magnetic resistance RE, RF.
, RG can be read as the magnetic resistance of each region E*, F*, G*, respectively.

In this case, the magnetic flux φ that generates leakage inductance is given by the following equation.

[Equation 1] Leakage inductance L generated from one coil 11 (12) of the sixth embodiment is given by the following equation.

[Equation 2] Here, the core material is selected so that the cross-sectional area A becomes A/a (a>1) while maintaining the magnetic resistance of the metatarsal core 48 at RF. In this case, the magnetic fluxes φ passing through the bypass magnetic paths are equal, so if the magnetic flux density of the sixth embodiment is B1 and the magnetic flux density of this embodiment is B2, the following equation holds true.

[Equation 3] Now, the saturation magnetic flux density of the bypass means 46 and 47 of the sixth embodiment is Bm, and the saturation magnetic flux density of the metatarsal core 48 of this embodiment is Bm.
Let it be m'. Then, when comparing the magnetic flux densities at the same NI value, from (Equation 3), Example 7 has a
The magnetic flux density is doubled. Therefore, in order to saturate both at the same NI value, it is necessary to satisfy the following conditions.

[Equation 4] In other words, if the magnetic resistance of the core for the bypass means is kept equal to that of Example 6, and a material with a saturation magnetic flux density a times that of the material of Example 6 is adopted, the leakage inductance and the saturation NI value ( While keeping the saturation current value) equal to that of Example 6,
The cross-sectional area of the metatarsal core can be reduced to 1/a times that of Example 6. As a result, the choke coil can be made smaller.

[0032] Normally, the effective relative magnetic permeability of the bypass magnetic path is 5 to 5.
50, the magnetic permeability of the metatarsal core 48 may be lower than the material of the core 45. By increasing the saturation magnetic flux density, a narrower cross-sectional area can be achieved. For example, in Example 6, when the bypass magnetic path width is 5 to 10 mm, a 3% silicon steel plate with a thickness of 0.1 mm is used as the middle core 48.
There is a design example in which the width of the bypass magnetic path can be reduced to about 1 mm by stacking several layers.

FIG. 14 shows an eighth embodiment using two E-shaped cores shown in FIG. 6(b), in which the shape of the bypass means is tapered toward the center. When the cross-sectional area of the portion constituting the closed magnetic path is a, and the cross-sectional area of the bypass means 48 and 49 is b, the following relationship holds true. b<2a
(5)

FIG. 15 shows
FIG. 3 is a diagram showing the distribution (normalized value) of magnetic flux density Bx in the core when a coil is wound around a rod-shaped core having a length l and a magnetic field is applied. This characteristic has been described in many documents and is widely known. In the figure, the longitudinal direction of the rod-shaped core is taken as the x-axis, and the center position of the core is set to x=0. In addition, Bo is the magnetic flux density at the center position of the core, and B
x represents the magnetic flux density at an arbitrary position x. As is clear from the figure, the magnetic flux density becomes smaller at both ends of the rod-shaped core. Therefore, in Example 8, the cross-sectional area b of the bypass means 48 and 49 corresponding to the ends in FIG.
This allows the material constituting the core to be saved.

[0035]

[Effects of the Invention] As explained above, according to the present invention, since the choke coil is configured to intentionally increase leakage magnetic flux, not only the common mode noise current but also the normal mode noise current can be reduced. Can be done. Furthermore, the capacitance of the across-the-line capacitors Cx1 and Cx2 can be reduced, and when used in a noise reduction device for a switching power supply, this contributes to a reduction in component costs.

Furthermore, as in Example 7, if a material having a higher saturation magnetic flux density is used for the metatarsal core serving as the bypass magnetic path than that of the core constituting the closed magnetic path, the metatarsal core becomes smaller than that in Example 6. This has the effect that the choke coil and noise filter can be made smaller because the cross-sectional area of the choke coil and the noise filter can be made smaller.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a first embodiment of a choke coil according to the present invention.

FIG. 2 is an inductance model diagram of FIG. 1;

FIG. 3 is a model diagram of a space through which magnetic flux that generates leakage inductance passes.

FIG. 4 is a magnetic equivalent circuit diagram of the device of FIG. 3;

FIG. 5 is a diagram showing a modified configuration of the first embodiment of the present invention.

FIG. 6 is a configuration diagram of a second embodiment of the present invention.

FIG. 7 is a configuration diagram of a third embodiment of the present invention.

FIG. 8 is a configuration diagram of a fourth embodiment of the present invention.

FIG. 9 is a configuration diagram of a fifth embodiment of the present invention.

FIG. 10 is a configuration diagram showing a modification of the fifth embodiment of the present invention.

FIG. 11 is a configuration diagram of a sixth embodiment of the present invention.

FIG. 12 is a configuration diagram of a seventh embodiment of the present invention.

FIG. 13 is a model diagram of a space through which magnetic flux that generates leakage inductance passes.

FIG. 14 is a configuration diagram of an eighth embodiment of the present invention.

FIG. 15 is a diagram showing the distribution of magnetic flux density Bx in the core when a coil is wound around a rod-shaped core having a length l and a magnetic field is applied.

FIG. 16 is a circuit diagram of a conventionally known switching power supply device.

FIG. 17 is a detailed diagram of the filter circuit.

FIG. 18 is an explanatory diagram of noise near the filter circuit.

FIG. 19 is an explanatory diagram of the operation of the common mode choke coil L1.

[Explanation of symbols]

11, 12...Coil 21...Core 22, 23...Protrusion 45...Core 46, 47...Bypass means 48…Matatarsal core

Claims (5)

[Claims] Claim 1: A core (21) constituting a closed magnetic circuit, and two coils (11, 12) wound around different parts of this core.
) and provided with a magnetic material inside the closed magnetic circuit of the core,
Bypass means (22) that bypasses a part of the magnetic flux generated by the current flowing through the coil independently of the closed magnetic circuit.
A choke coil characterized by comprising the following. Claim 2: A core (45) constituting a closed magnetic path with a constant cross-sectional area (a), two coils (11, 12) wound around different parts of this core, and a closed magnetic path of the core. Bypass means (46 , 47), wherein the cross-sectional area of the bypass means is twice the cross-sectional area of the core or slightly smaller than this. 3. A core (45) constituting a closed magnetic path with a constant cross-sectional area (a), two coils (11, 12) wound around different parts of this core, and a closed magnetic path of the core. Bypass means (48 ), the magnetic material of the bypass means is made higher than the saturation magnetic flux density of the magnetic material of the core, and the cross-sectional area of the bypass means is made smaller than the cross-sectional area of the core. Choke coil. 4. The choke coil according to claim 1, 2 or 3 is connected to an alternating current power source, the applied alternating current is converted to direct current by a rectifying and smoothing circuit, and the converted current is converted to direct current by a switching power source. A noise reduction device for a switching power supply device, characterized in that a DC voltage of a predetermined voltage is supplied to a load side. 5. The alternating current sent from the alternating current power source is converted into direct current by a rectifying and smoothing circuit, and the converted current is supplied to the switching power source via the choke coil according to claim 1, 2, or 3. A noise reduction device for a switching power supply device, characterized in that a switching power supply converts the DC voltage to a predetermined voltage and supplies it to the load side.